The problem of treatment and disposal of the municipal organic waste materials, food wastes and animal wastes, such as animal carcasses and road kill, has been a challenge to nations, municipalities and industries since the dawn of civilization. There is a growing critical problem for human health risks due to an increasing variety of communicable diseases and pathogenic agents including fungi, bacteria, viruses and transmittable spongiform encephalopathy (TSE). The recent crisis in Europe relating to TSE diseases such as Mad Cow Disease, has accelerated the need for a benign technology which will inactivate and denature these rogue protons (called prions).
Traditionally, processing of organic waste materials entailed aerobic or anaerobic treatment and/or digestion of the materials, and stabilization of the digested materials. For sewage wastewater, additional steps, such as clarification and stabilization, are required, utilizing settling ponds or tanks, and followed by dewatering in lagoons or with mechanical dewatering systems to yield sewage sludge before final disposal. Incomplete inactivation of pathogenic agents in the organic materials occurred primarily at the thermophilic stage during the digestion process. The conventional waste processing or disposal, however, does not guarantee sterilization of pathogens present in the organic materials, requires enormous land areas for lagoons and settling ponds or for landfills, as well as a period of weeks to months for completion, and presents air and water pollution, nuisance and other problems for the surrounding environment.
A number of other waste treatment methods have been tried over the years with varying degrees of success. They include the following types:
Heat treatment is a process used for disinfection and sterilization of sewage sludge. During heat treatments, enteric viruses in the waste materials are expected to be deactivated at or above 70.degree. C. according to established guidelines of the United States Environmental Protection Agency. The method has been claimed effective in destroying most enteric pathogens in waste materials, especially sewage sludge, over an extended period of time.
Ionizing radiation has also been tried as a method to sterilize sewage sludge. 600-850 keV gamma radiation can be employed at dose levels of 1 Mrad to destroy pathogens present in the sewage sludge. .sup.60 Co and .sup.137 Cs are prime sources of the gamma radiation. A system which uses gamma radiation has been developed by Nordion International of Kanata, Ontario, Canada. This system, however, requires high capital expenditures and, furthermore, alters the physical and chemical properties of the sludge. X-ray and ultraviolet radiation have also been used in efforts to disinfect waste materials, but the results showed that the radiation is effective only for indicator microorganisms, such as coliform, and not effective for most pathogens such as gadia and cholera vibro. These latter agents present greater risk to human health.
Incineration is another organic waste treatment process where temperatures in excess of 1,200.degree. C. are used to completely oxidize the biomass or sludge. If all genetic materials associated with microorganisms are destroyed, the opportunity to recycle sterile organic materials increases the cost-effectiveness of the treatment process. There is, however, still a need to dispose of residues from the incineration operation and incineration facilities are expensive. In addition, air emissions from incineration remain a major environmental concern.
Chemical disinfection is also used in treating liquid wastes. Chlorine compounds, ozone, and other sterilizing substances are used to treat liquid wastes. The chemical treatment may produce residues such as chlorinated hydrocarbons which themselves have to be treated or disposed.
Fumigation using certain toxic gasses is also used to inactivate fingi, bacteria, viruses and other pathogens. While a number of substances have been evaluated for their effectiveness in disinfection or sterilization, application of this technology requires great care to prevent human exposure to the toxic gaseous chemicals through inhalation.
Composting utilizes enhanced aerobic biological activities to stabilize organic wastes. Composting processes may vary with the raw materials and the technologies. There are a variety of composters ranging from composting piles to automated composting chambers. A composting facility may take all types of organics and biomass materials and the operation can be continuous if a plug flow process is designed. It may take from a few days to a few weeks for the compost to mature. Construction costs of a well engineered composting facility can be high and the operation requires a good emission control system to protect the health of the operators.
U.S. Pat. No. 3,385,687 demonstrates composting of comminuted municipal organic wastes in a digester. The nitrogen to carbon ratio in the composted product is at least 1:20. U.S. Pat. No. 3,533,775 discusses use of mixtures of comminuted municipal waste and sewage sludge to make fertilizer. As instructed therein, sewage sludge is mixed with municipal waste to provide a uniform mixture. Thereafter, the mixture of sludge and comminuted waste is aerobically digested. The resulting materials are dried and ground for lawn treatment and other uses. Disposal of sewage sludge by composting the sludge with ammonia is shown in U.S. Pat. No. 3,442,637. Disposal of mixed sewage sludge with shredded municipal waste is shown in U.S. Pat. No. 4,586,659. The resulting mixture is sent to a composter and treated with aerobic bacteria to yield a product useful as a soil conditioner. Composting is not suitable for processing animal carcasses, as composting does not disinfect or sterilize the pathogenic agents contained in the materials to be processed.
Landfilling and landspreading are common. Disposal of animal by-products, diseased carcasses, hide trims, skulls, and hooves from meat processing plants traditionally has been performed by landfilling. Manure is usually stockpiled and spread over fields. Although these materials may be useful as agriculture fertilizers, stockpiling, landfilling, and landspreading of these materials create human health risks. These include air pollution, and groundwater contamination from runoff and provide the breeding grounds for disease-carrying vectors such as flies. Disposal of animal carcasses or other infectious animal wastes, such as hide trim, rotten eggs and the like which are more likely to contain infectious microorganisms, traditionally entailed landfilling. This method, although being cost effective in some places, suffers the disadvantages of contaminating the environment and putting human health at risk. Landfilling and landspreading are not effective for disinfection or eradication of pathogens contained in municipal organic wastes and animal wastes, sewage sludge and other organic wastes, and require extended time periods and large land areas or lagoons. The products of the prior art treatments are, moreover, malodorous and are not sterile. Sterility is desired because of the typical presence of pathogenic organisms in the materials. The end products need to be sterile before being put on the market.
With the eruption of transmittable spongiform encephalopathy (TSE), particularly bovine spongiform encephalopathy (BSE) and scrapie diseases in Europe, inactivation of pathogenic agents is even more necessary. Animal wastes, such as offal, paunch manure and carcasses, are subject to carrying infectious agents including fungi, bacteria, viruses and prions associated with BSE, TSE, etc. A need therefore exists for methods of processing and/or disposal of municipal organic waste materials, sewage sludge, and animal waste without the disadvantages of the prior art.
The present invention overcomes all the disadvantages and problems of the prior art by efficiently treating and processing the various kinds of organic waste products discussed above, in combination with a fibrous material, which fibrous material may be, but need not be obtained from municipal solid organic waste, which is also becoming an environmental burden as landfills are reaching their capacities and waste production is increasing. The present invention involves refining and denaturing the infectious organic waste material and using organic fibrous materials such as newspapers, corrugated cardboard, or even waste organic fibrous material such as mixed waste packaging material, or dried plant products. The inventive bio-refining method for treating a wide variety of waste materials produces sterile, inactive or denatured and environmentally-friendly end products, such as soil conditioners or fertilizers or other useful materials. The invention utilizes saturated steam at elevated temperature and pressure during the denaturing and sterilization process to denature all potential pathogenic agents. Malodorous vapors are evacuated from the headspace in the treatment vessel, condensed, and scrubbed, using commercially available wet and dry scrubbers from companies such as American Air Filter, Louisville, Ky., U.S.A. The treatment time necessary to achieve these results is short, being a matter of hours, particularly when compared to prior art technologies employed for waste processing which can take days.